Dual output phase shifter



m a .419 e22- y 1 s. N. ANDRE ETAL 3,419,822

I DUAL OUTPUT PHASE SHIFTER 7 Filed Dec. 30,- 1966 Sheet of 2 PoRT I20 PoRT 12b dab ,Q L MODE TRANSDUCER sLow PLANE QUARTER wAvE PLATE FAST PLANE FARADAY RoTAToR m H 111 m L. L? Q o b o b o b Pb Q/ (Do 2 o REF. D

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STEPHEN N. ANDRE and LELAND R. MEGARGEL ATTORNEY.

Dec. 31 19% S. N. ANDRE ET AL DUAL OUTPUT PHASE SHIFTER z of 2 I Sheet Filed Dec. 30, 1966 COMPONENT 226 SHORT CIRCUIT TO TE INVENTORS. STEPHEN N. ANDRE and LELAND R. MEGARGEL BYI-M M. W

ATTORNEY.

llnited States atent Qfitice Patented Dec. 31, 1968 3,419,822 DUAL OUTPUT PHASE SHIFTER Stephen N. Andre, Tonawanda, and Leland R. Megargel, Buffalo, N.Y., assignors to Sylvania Electric Products Inc., a corporation of Delaware Filed Dec. 30, 1966, Ser. No. 606,314 2 Claims. (Cl. 333-41) ABSTRACT OF THE DISCLOSURE A phase shifter comprising a circular waveguide assembly containing a Faraday rotator and a quarter wave plate disposed in that order between a single input port and a dual mode transducer having two output ports. A resistive card is axially disposed at the input end of the guide to absorb the reflected TE component. The output ports are oriented at 45 on either side of the fast plane of the quarter wave plate and spaced from each other along the longitudinal axis of the guide to provide decoupling. A series of three transverse wires are located between the output ports to short circuit the TE component having the polarization to which one of the output ports is receptive.

This invention relates generally to phase shifters and, more particularly, to an electrically controllable ferrimagnetic phase shifter for providing more than one output signal.

Electrically controllable phase shifters are employed in a variety of applications for varying the phase of a radio frequency (RF) voltage, With respect to the phase of the source voltage, in response to a direct current or low frequency control signal voltage applied to the phase shifter. Such devices are particularly useful in the control of phased array antennas. The beam formed by a stationary array of antenna elements can be steered by varying the relative phase of the RF voltages supplied to each of the elements. Rapid beam movement in response to steering commands requires a phase control device that will respond quickly to steering information. The electrically variable ferrite phase shifter has been developed to perform this function.

An application toward which the present invention is particularly directed is that of providing phase control for a microwave antenna including a symmetrical ring array which scans continuously through 360 in one plane; such an antenna system is described in copending application Ser. No. 606,181, filed Dec. 30, 1966 and assigned to the assignee of the present application. The operation of this antenna requires that diametrically opposite elements of the ring array be supplied with instantaneously equal voltages having phase angles which are equal in magnitude and opposite in sense. The phase angles are required to vary through both positive and negative values about a quiescent reference level.

Conventional phase shifters, of either coaxial or waveguide construction, provide only a single output and, if of the reciprocal ferrite type, must be biased in order to obtain phase angles of both senses. Non-reciprocal devices that do not require bias have been made in rectangular waveguide, but they also provide only one output. A ferrite version of the Fox half wave plate mechanically operated phase shifter has been described in the literature, but this device requires a magnetic structure similar to a four-pole two-phase alternating current motor. The radio frequency phase angle produced by the shifter corresponds in magnitude and sense to the angle through which the transverse magnetic field of the motor type field structure is rotated by the relative amplitude and phase separation of the two control voltages, and in addition, the

With an awareness of the foregoing limitations and disadvantages of conventional phase shifters, it is an object of the present invention to provide an electrically controllable phase shifter capable of highly efiicient operation and producing more than one output signal.

Another object of the invention is to provide an electrically controllable ferrimagnetic phase shifter capable of producing a pair of conjugately phased outputs from a single input voltage.

Briefly, these and related objects are achieved by means of a phase shifter which employs the Faraday rotation phenomena in conjunction with a 90 differential phase shift transmission line section and a dual mode transducer to produce two equal amplitude radio frequency outputs from a single input. The phase angles of the outputs are equal in magnitude and opposite in sign. The phase shifter requires a relatively small amount of control power, and the phase of each output is a linear function of the control signal voltage applied to the Faraday rotator.

Other objects, features and advantages of the invention will become apparent and its construction and operation better understood from the following detailed description, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic representation of a phase shifter in accordance with the invention;

FIG. 2 is a combined schematic and vector diagram illustrating four conditions of operation of the phase shifter shown in FIG. 1;

FIG. 3 is a plan view of a preferred embodiment of the phase shifter of FIG. 1;

FIG. 4 is a cross-sectional view taken along line 44 A of FIG. 3, with the solenoid not shown, which illustrates the interior structure of the phase shifter;

FIG. 5 is a cross-sectional view taken along line 5-5 of FIG. 3 which illustrates the input structure of the phase shifter;

FIG. 6 is a cross-sectional view taken along line 66 of FIG. 3 which illustrates the manner in which a ferrimagnetic rod is supported within the phase shifter; and,

FIG. 7 is a cross-sectional view taken along line 7-7 of FIG. 3 which illustrates the structure of a quarter wave plate which forms part of the phase shifter.

Referring to the schematic representation of FIG. 1, the phase shifter is shown as a waveguide assembly comprising a Faraday rotator 10, a dual mode transducer 12 having a pair of output ports 12a and 12b, and a quarter wave plate 14 having fast and slow planes of propagation. In FIG. 1, the fast plane is a vertical plane cutting longitudinally through the center of the waveguide, while the slow plane is a horizontal plane cutting longitudinally through the center of the waveguide.

The electromagnetic wave energy incident at the input to the Faraday rotator is plane polarized as indicated by the electric field vector E The Faraday rotator 10 is responsive to application of an axial static magnetic field of intensity H to produce a rotation of the plane of,polarization through an angle 6, the rotated electric field vector being denoted as E This rotational effect changes the angle of polarization with respect to the fast and slow planes of the quarter wave plate 14. A wave passing through the quarter wave plate polarized in the slow plane is delayed ninety electrical degrees with respect to a wave of identical phase and frequency entering the plate and polarized in the fast plane. If periodic waveform control signals are applied to the phase shifter to control the magnetization of the Faraday rotator, a plane polarized wave of variable polarization angle is produced and impinges upon the quarter wave plate. The dual mode transducer 12 following quarter wave plate 14 is oriented to extract separately the two orthogonal polarizations which are in clined 145 to the fast plane of the quarter wave plate.

The operation of the phase shifter will now be analyzed with reference to FIG. 2, which illustrates four conditions of polarization of the wave impinging upon the quarter wave plate 14, denoted as I, II, III, and IV. Each polarization condition is illustrated by a schematic axial view of the phase shifter waveguide looking in the direction of propagation, with the arrow indicating the electric field vector. Below each schematic is a corresponding vector diagram to further clarify the relative positions of the E field vector impinging on the quarter wave plate, the electric field vector in port 12a, the output of which has a phase denoted as (pa, and the electric field vector in output port 12b, which has an output phase denoted as qfib.

If the output wave of rotator is polarized in the fast plane of quarter wave plate 14, as in condition I, all the energy passes through the quarter wave plate with a minimum delay and divides equally between the two outputs. Consequently, the two output phases a and b are equal.

If the rotator output polarization is rotated 90 clockwise to lie in the slow plane of the quarter wave plate, as illustrated in condition II, all energy transmitted by the quarter wave plate is delayed 90 with respect to the zero reference condition 1. Again the output of the quarter wave plate divides equally between the two output ports. The component in port 12a is directed in the same spacial direction. but has been retarded 90 by the quarter wave plate so that a now equals 90. The component in port 1212 is oppositely directed in the spacial sense so that it can be considered to have been advanced in phase 180; however, since this component has also been retarded 90 by the quarter wave plate, b equals +90".

An additional 90 rotation of the rotator output, as shown in condition III, is identical to the starting condition I except that both output vectors are reversed; hence, a equals -lSO and b equals j+180.

Finally, referring to condition IV, a 270 rotation of the E vector is identical to condition 11 except that both output vectors are reversed. In this case, the output phases are 270 for (pa and +270 for 6b.

For the continuous variation of the rotator output polarization between the four specific cases illustrated above, it may be stated that, in general, each output is composed of an undelayed and a 90 delayed component. The undelayed component. The undelayed E field component of the output of the quarter wave plate is E cos 9, and the 90 delay component is E sin 0, where E is the field strength of the E vector.

The total E field in port 12a is at angle 0a=ta (-sih 0) cos 0 0 at, angle 0b=t-au (sin 0) cos 6 The E field in port 121) is sin D l -E (me 0 In its simplest form, the Faraday rotator consists of a square or circular waveguide having a long slender ferrite rod positioned along the axis of the guide. A solenoid pro duces an axial magnetic field. The direction in which the plane of polarization of a plane polarized wave is turned depends upon the direction (sense) of the control field and the direction in which the wave is propagating.

The amount of Faraday rotation obtainable per unit length of the rod is dependent upon the magnetization produced in the ferrite, the amount of ferrite present and the energy distribution inside the ferrite loaded guide. This tagnetization depends upon the applied field strength, the

ferrite composition, and the ferrite geometry. The energy distribution is dependent upon the ferrite and guide geometries, the dielectric constant of the ferrite and the medium surrounding it, the percentage of the guide cross section occupied by the ferrite, and the frequency of the electromagnetic wave energy. Although the rod to be magnetized in the rotator has been described as being composed of ferrite material, any other material demonstrating ferrimagnetic properties may be employed, such as garnet.

A preferred embodiment of the above described phase shifter intended for operation at X-band is illustrated in the diagrammatic views of FIGS. 3 thru 7. In this particular design, the Faraday rotator, quarter wave plate and dual mode transducer are assembled in a circular waveguide 16 having an input port 18 and a pair of orthog' onally disposed output ports 20 and 22. Each of the ports 18-22 includes a coaxial connector having a microwave probe protruding into the circular waveguide; the probes are respectively denoted as 18a, 20a, and 22a. Waveguide 16 is a tubular conductor, such as silver coated copper, having an inside diameter of about 0.7" and a length of about 12.5. Circular plates 24 and 26 are securely brazed or soldered to the ends of the tubular waveguide. The Faraday rotator comprises a 5 /2" long ferrimagnetic rod 28, which can be constructed in a plurality of segments, supported along the axis of circular waveguide 16 by conductive vanes 30 and dielectric end plugs 32. The rotator further includes a solenoid coil 34 wound around the outside of the waveguide 16 to produce an axial magnetic field within the rod 28 when the solenoid is electrically energized. Wire ends 34a and 34b represent the terminals through which control signals are applied, from a suitable source (not shown), to energize solenoid 34.

To provide the desired performance, ferrimagnetic rod 28 is of a segmented construction made up of several garnet cylinders cemented together, each cylinder being A2 long and A1 in diameter. Four conductive vanes 30 are symmetrically arranged as shown in FIG. 6 to support rod 28 along the central axis of the waveguide, each of the vanes being soldered or otherwise secured to the walls of the waveguide cylinder to ensure a good electrical connection thereto. The dielectric end plugs 32, which also provides support for rod 28, are recessed to receive respective ends of the rod, and the outside diameter of each plug is tapered toward this recess opening.

The quarter wave plate in this instance is of the lumped susceptance type comprising three pairs of diametrically opposed screws or rivets protruding into the circular waveguide at a 45 angle with respect to'output probes 20a and 22a; screws 36a, 38a, and 40a are shown in FIG. 3, while the pair 38:: and 3811 are ,shown in FIG. 7. Screws 36b and 40b are not visible in the drawings. The slow plane of the quarter wave plate is the plane cutting longitudinally through the structure 16 and through the protrusions in the waveguide, denoted by edge line S in FIG. 7. The fast plane is normal to the slow plane and passes between theprotrusions, as denoted by edge line F in FIG. 7.

In FIG. 1, the dual mode transducer is schematically illustrated as having orthogonally related waveguide junc tions providing output ports 12a and 12b. In FIG. 3, an alternate embodiment is shown wherein the dual mode transducer corn-prises orthogonally oriented probes 20a and 22a in circular waveguide 16. Referring to FIGS. 3, 4, and 7, it will be noted that probes 20a and 22a are oriented at 45 on either side of the fast plane of the quarter wave plate, the orientation of the fast plane being denoted by intersection line F. In addition, probe 22a is displaced along the longitudinal axis of the waveguide from probe 20a to provide decoupling. During experimentation, it had been determined that with the orthogonal probes located in the same plane, coupling between-the adjacent probes was caused by TM standing waves existing in the region near the probes. Further, a series of three transverse wires 42 are located between the coaxial probes and parallel to probe 20a to function as a quarter wave short to the TE component having the polarization to which probe 20a is receptive, while exerting virtually no effect upon the perpendicularly polarized component.

Referring to FIGS. 3 and 5, a resistive card 44 is located axially at the input end of the waveguide in a plane perpendicular to probe 18a and spaced away from the end of that probe. The resistive card is employed to absorb the reflected field perpendicular to the field launched; i.e. the TE component having a polarization in the plane of the resistive card. To enable a reduction in the diameter of the waveguide 16, the guide is filled with a solid dielectric 46, except for the space between end plugs 32. An air space separates vanes 30 about rod 28 within waveguide 16.

In operation, application of electromagnetic energy to input port 18 causes a linearly polarized wave to be launched into the Waveguide from input probe 18a. When a sinusoidal control current is applied via wires 34a and 34b thru solenoid 34, an axial magnetic field is produced within rod 28 which causes the plane of polarization of the incident wave to be rotated as a function of the strength of the magnetic field. This Wave of rotating polarity is converted to a circularly polarized wave after passing through the quarter wave plate. The orthogonally oriented output probes 20a and 22a extract conjugately phased outputs from the phase shifted circularly polarized wave for application to output loads. The amount of phase shift is governed by and is approximately a linear function of the magnitude of the control voltage applied to the solenoid of the rotator.

In an application of this phase shifter at X-band, the control field produced by a 2178 turn solenoid wound in six layers with AWG No. 28 wire enabled :360 of phase shift to be obtained using less than 0.1 watt of control power. The segmented construction of the rod 28 was found to reduce the magnetic hysteresis within the rod, and the use of the vanes 30 contributed substantially toward the linearization of rotation with magnetic field strength. When plotting the amount of Faraday rotation produced by this device as a function of magnetic field strength, or coil current, the resulting curve had the form of a magnetic hysteresis loop. The slope of either side of this loo was approximately of rotation per milliampere of coil current. Rotation axis intercepts corresponding to zero applied field occurred at :20". Peak applied fields were approximately +14 ampere turns per inch. The measured insertion loss was less than 1 db. In addition to these electrical advantages, the described phase shifter provides a light package, less than 12 ounces, which is mechanically and electrically rugged.

While a particular embodiment of the invention has been illustrated and described, it is understood that the applicant does not wish to be limited thereto since modifications will now be suggested to ones skilled in the art. For example, other Faraday rotator configurations may be employed, and the differential phase shift section (quarter wave plate) may be implemented in a variety of ways. The invention, therefore, is not to be limited except in accordance with the appended claims.

What is claimed is:

1. An electrically controllable phase shifter for producing a pair of output signals comprising, a waveguide structure having a closed input end and a closed output end, an input terminal at said input end adapted to couple electromagnetic energy into said Waveguide structure, a Faraday rotator including a ferrimagnetic rod coaxially disposed within said structure adjacent to said input end and a solenoid disposed around a portion of said structure and coextensive with said rod, a pair of output terminals at said output end adapted to couple energy from said structure and oriented orthogonally with respect to each other and with one output terminal being coplanar with .said input terminal, and a quarter wave plate disposed within said structure between said rotator and said output terminals and including pairs of diametrically opposed protrusions extending into the waveguide structure and oriented in a longitudinal plane through said structure which is midway between longitudinal planes intersecting said output terminals.

2. A phase shifter comprising, in combination, a circular waveguide, a Faraday rotator including a ferrimagnetic rod coaxially positioned within said waveguide and a solenoid arranged to produce an axial magnetic field within said rod when electrically energized, a plurality of conductive vanes supporting said ferrimagnetic rod along the axis of said waveguide, an input port for coupling applied electromagnetic energy to said Faraday rotator, said input port comprising a coaxial connector having a microwave probe protruding into said circular waveguide, a resistive card disposed axially at the input end of said waveguide in a plane perpendicular to said input probe and spaced awayfromthe end of that probe, said card functioning to absorb the reflected field perpendicular to the field launched from said input probe, a dual mode transducer having two output ports each of which comprises a coaxial connector having a microwave probe protruding into said circular waveguide, a quarter wave plate disposed within said waveguide between said rotator and said transducer and having fast and slow planes of propagation, said two output probes being oriented orthogonally with respect to each other and oriented at 45 on either side of the fast plane of said quarter wave plate, one of said output probes being displaced along the longitudinal axis of said waveguide from the other of said output probes to provide decoupling, and a plurality of transverse wires disposed between said output probes and parallel to one of said output probes to function as a quarter wave short to one of the components of the electromagnetic wave propagating through said waveguide.

References Cited UNITED STATES PATENTS 8/1956 Olive 3336 X 5/1963 Allen 333-241 X U.S. Cl. X.R. 333--24.1, 24.3 

